This project will study in humans how the awareness of static limb-position and the sense of limb-movements are derived from sensory inputs from joint, skin and muscle, the tests involve matching of one limb or digit to its opposite, detecting movements, or misalignments from the matched position, and estimating the magnitude of a misalignment or the speed of a movement. Using healthy, adult volunteer subjects, tests will first be done to develop procedures that can distinguish movement sense and position sense, and then to establish baseline performance levels. Evidence indicates these two senses are different. The effect of eliminating various inputs using local anesthetic block will then be tested. Some tests will use patients having a complete rupture of the achilles tendon. A major goal is to test the hypothesis that muscle spindles provide the necessary and sufficient sensory input for limb position sense, and that skin and joint contribute little or nothing. The hand is an exception, cutaneous inputs are in some way involved in kinesthesia in the fingers, but not in other joints like the knee. How the hand differs in this and other respects will be tested. Finally, whether gamma control of spindle activity is essential to position accuracy will be tested in subjects with: a) relaxed muscles, and b) partial (gamma) block of motor nerves and c) using recordings from spindle afferents in humans to see if there is a change (reflecting gamma activity) during position discriminations. Once we know the source of the position and movement detectors, and more about coding and fusimotor control, we will be in a position to do meaningful experiments on animals for detailed neurophysiological research.